1. Field of the Invention
The present invention relates to a torque split type automatic transmission which is applied to vehicles. More particularly, the present invention relates to a torque split type automatic transmission which increases torque by transmitting the torque output from an engine through two paths and adding the torque passing through each path.
2. Description of Related Art
Recently, engine output increases by 20-30% compared with a conventional engine with the same exhaust amount and size due to development of engine technologies.
Since a conventional transmission includes only one power delivery path, all the torque of the engine is directly transmitted to a launching device such as a torque converter or a clutch. Therefore, if the engine output increases, design of the transmission must be changed so as to increase torque delivery capacity.
In order to increase the torque delivery capacity, strength of an axle must be strengthened and the number of friction members must be increased due to characteristics of a power delivery device. However, if the strength of the axle is strengthened, weight of the axle should be increased. In addition, if the number of the friction members is increased, size of the transmission should be increased. Therefore, fuel consumption and power performance of a vehicle may be deteriorated due to increase in the weight of the axle and installability of the transmission may be deteriorated due to increase in the size of the transmission.
Since it is needed to change a design of the launching device such as the torque converter in order to increase torque capacity thereof, much development cost and time is needed.
Recently, a torque split type transmission which transmits the torque through at least two power delivery paths is developing. The torque split type transmission has a merit that the torque capacity can increase with a few changes in the design.
Some examples of the torque split type transmission are described in U.S. Pat. Nos. 4,014,223, 4,117,745, and 4226123 having a power delivery path shown in FIG. 5A and in U.S. Pat. No. 5,201,692 having a power delivery path shown in FIG. 5B.
The torque split type transmission shown in FIG. 5A includes a first path in which the engine torque is indirectly delivered to a transmission device 112 through a planetary gear set which is a torque split device 110 and a torque converter which is a launching device 111 and a second path in which the engine torque is directly delivered from the planetary gear set 110 to the transmission device 112. The torque increased in the torque converter which is the launching device 111 is added to the torque transmitted from the torque split device 110 to the transmission device 112, and final torque is output to a driving wheel through the transmission device 112.
According to the torque split type transmission shown in FIG. 5B, the engine is increased in the torque converter which is the launching device 120. After that, the torque is dividedly delivered to the driving wheel through the planetary gear set of the torque split device 121 and to a continuously variable transmission of the transmission device 122. The torque output from the transmission device 122 is added to the torque delivered from the torque split device 121 to the driving wheel.
According to the torque split type transmission shown in FIG. 5A, all the increased torque is delivered to the transmission device and it may cause problems in the torque delivery capacity of the transmission device.
According to the torque split type transmission shown in FIG. 5B, the continuously variable transmission is used as the transmission device. If large torque is delivered to the continuously variable transmission, torque split efficiency may be deteriorated.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.